The present invention relates to smoking articles such as cigarettes, and in particular, to those smoking articles having a short fuel element and a physically separate aerosol generating means. These smoking articles are capable of providing the smoker with the pleasures of smoking (e.g., smoking taste, feel, satisfaction, and the like). The invention particularly relates to improved methods for making improved substrates for use in such smoking articles.
Cigarettes, cigars and pipes are popular smoking articles which use tobacco in various forms. Many products have been proposed as improvements upon, or alternatives to, the various popular smoking articles. For example, numerous references have proposed articles which generate a flavored vapor and/or a visible aerosol. Most of such articles have employed a combustible fuel source to provide an aerosol and/or to heat an aerosol forming material. See, for example, the background art cited in U.S. Pat. No. 4,714,082 to Banerjee et al.
A number of smoking articles have been designed and produced having a short carbonaceous fuel element and a physically separate aerosol generating means. Smoking articles of this type, as well as materials, methods and/or apparatus useful therein and/or for preparing them, are described, for example, in U.S. Pat. No. 4,708,151 to Shelar; U.S. Pat. No. 4,714,082 to Banerjee et al.; U.S. Pat. No. 4,732,168 to Resce; U.S. Pat. No. 4,756,318 to Clearman et al.; U.S. Pat. No. 4,782,644 to Haarer et al.; U.S. Pat. No. 4,793,365 to Sensabaugh et al., and the patents cited in U.S. Pat. No. 5,546,965, the disclosures of which are incorporated herein by reference.
Many of the smoking articles described in the prior art employ a combustible fuel element for heat generation and an aerosol generating means positioned physically separate from, but often in a heat exchange relationship with, the fuel element. The aerosol generating means typically includes one or more aerosol forming substances such as glycerin and a carrier or substrate therefor. During smoking, heat generated by the fuel element acts to volatilize the aerosol forming substances, thereby providing an aerosol which resembles tobacco smoke.
Many of the prior art smoking articles employ a substrate as a carrier for the aerosol forming substance in the aerosol generating means. Typically these substrates have been noncombustible solids, e.g., graphite, carbon, alumina, and the like, which are deemed heat-stable under the operating conditions of the smoking articles using them. In such articles the substrate was exposed to temperatures in the range of 400xc2x0-800xc2x0 C., necessitating a heat-stable material. In U.S. Pat. Nos. 5,182,062 and 5,203,355 the substrate material was a cellulosic material such as a gathered paper, bearing an aerosol forming material at a loading level ranging from about 100% to about 400% by weight.
Such smoking articles often additionally include tobacco in various forms such as cut filler, reconstituted tobaccos, densified pellets, tobacco dust and tobacco extracts, as well as tobacco flavor modifiers and tobacco flavoring agents. Such tobacco components are included in addition to the substrate bearing the aerosol forming material, which is the prime source of aerosol former for smoke generation. The tobacco components can also add aerosol and/or flavorants to the smoke generated by the substrate, to enhance the volume, flavor, or other qualities of the smoke ultimately provided to the smoker.
Some such smoking articles have previously utilized tobacco supersaturated with aerosol forming materials as substrates. Such substrates provided good quantities of aerosol, but were difficult to make and difficult to incorporate into the smoking articles.
Indeed, substrates for use in such smoking articles, whether or not they incorporated tobacco, have tended to be expensive to make and difficult and expensive to manufacture into the finished product. Aerosol formers, such as glycerin, tended to migrate from the substrates, especially if the substrates were loaded with high amounts of the aerosol former, so that a visible wet ring of aerosol former would often form around the substrate portion of the smoking article. Migration of substrate could also have a deleterious effect on the storage or shelf-life of the smoking articles, which typically have to be stored for extended periods in warehouses which are often hot, or otherwise conducive to loss of aerosol former. Typically smoking articles should be able to produce adequate aerosol even after storage for up to seven months at 88xc2x0 F. and 80% relative humidity.
The present invention represents an improvement in substrates for smoking articles, wherein the heat-stable substrate is wholly or partially replaced by tobacco or tobacco-containing compositions, which themselves bear a high load of aerosol former. The invention is particularly directed to methods of making improved tobacco substrates containing substantial amounts of aerosol formers, and of making smoking articles incorporating such substrates.
The present invention provides improved substrate material for cigarettes and other smoking articles employing short fuel elements and physically separate aerosol generating means. The substrate is a tobacco material bearing a substantial amount of an aerosol forming composition. The tobacco substrate is manufactured in a way which permits it to be made into substrate elements for inclusion in smoking articles in a manner similar to the manufacture of tobacco cigarettes.
The substrates of the present invention are tobacco materials; that is, they primarily comprise tobacco, although additives and fillers may be included in the substrate. Preferred tobacco materials used as substrates herein are flue cured, Turkish, expanded tobacco, expanded stems, and traditional blend ratios of the known tobacco types. Preferably the tobacco utilized in the substrate is cellular tobacco material, e.g., cut tobacco leaf or the like, in which a substantial percentage of the tobacco plant cells remain. Other types of tobacco, such as reconstituted tobacco sheet, can be added in minor proportions for flavor enhancement, but it is preferred that the majority of the tobacco be cellular tobacco material.
The preferred type of tobacco used for the substrates of the present invention is flue-cured tobacco, particularly tobacco which has been cured using heated air only, without substantial contact with products of combustion of the fuel used to heat the air.
Prior to conversion into the substrate material of the present invention, the tobacco may be in the forms of sheets, webs, strands, filaments, strips, shredded tobacco and the like. Preferably, the substrate material starts as strip tobacco, which is the form of tobacco produced when tobacco leaf is deveined. The strip tobacco is contacted and infused with aerosol former. Preferably such contact takes place in a casing drum, which is a rotating drum liquid/solid contact device. Casing drums are known per se in the tobacco industry, and have long been used to add relatively small amounts (e.g., about 3%-6% by weight) of moisture, emollients (including glycerin) and/or flavorants to tobacco. The tobacco material is preferably continuously fed to one end of the rotating drum, which has a series of baffles to agitate and convey the tobacco to the other end of the drum.
As the tobacco traverses the rotating drum, it is intimately contacted by aerosol former in liquid form, whereby the aerosol former becomes sorbed by the tobacco material. The aerosol former is in liquid form, preferably in an aqueous solution, since the presence of water typically reduces the viscosity of the aerosol former, which aides in penetration of the aerosol former into the tobacco material. Preferably the aerosol former solution is applied by pressure nozzles spaced throughout the casing drum. Alternatively or additionally, steam can be injected into the casing drum to heat and humidify the tobacco being processed, thus improving infusion of the aerosol former.
Preferred aerosol formers include the polyhydric alcohols, such as glycerin, propylene glycol, triethylene glycol and tetraethylene glycol), the most preferred being glycerin. Other aerosol formers may also be used, such as the aliphatic esters of mono-, di- or poly-carboxylic acids (e.g., methyl stearate, dimethyl dodecandioate, and dimethyl tetradcanedioate), Hystar TPF, available from Lonza, Inc., and the like, as well as mixtures of any of those materials.
Preferably the aerosol former is applied in the form of an aqueous solution containing about 40% to about 90% by weight aerosol former, with the balance water. Preferably the aerosol solution contains about 70% to about 80% by weight glycerin, most preferably about 75% by weight glycerin. While addition of water helps reduce viscosity of the glycerin, addition of too much water prevents the tobacco from taking the high loading of aerosol former. Moreover, most of the water picked up by the tobacco in this process has to be removed before the material can be used as a substrate in a smoking article.
The aerosol former solution is preferably heated in order to further enhance infusion of the aerosol former into the tobacco. The temperature of the solution can vary from about 100xc2x0 F. (about 38xc2x0 C.) to about 150xc2x0 F. (about 66xc2x0 C.), preferably about 120xc2x0 F. (about 49xc2x0 C.) to about 140xc2x0 F. (about 60xc2x0 C.), most preferably at about 130xc2x0 F. (about 54xc2x0 C.).
Optionally, or additionally, the tobacco can also be heated and humidified by injection with steam during the infusion of the aerosol former solution. Sufficient steam is injected into the casing drum to raise the tobacco temperature to about 100xc2x0 F. (about 38xc2x0 C.) to about 160xc2x0 F. (about 70xc2x0 C.), preferably about 120xc2x0 F. (about 49xc2x0 C.) to about 140xc2x0 F. (about 60xc2x0 C.), most preferably at about 130xc2x0 F. (about 54xc2x0 C.).
The amount of aerosol former solution applied to the tobacco is determined by the desired loading of the resulting tobacco. Thus the feed rate of the aerosol former liquid is adjusted, in accordance with the feed rate of the tobacco to the casing drum, to provide the proper loading level on the resultant tobacco substrate. Preferably a small excess of aerosol former is applied to the tobacco, to make up for aerosol former lost during the process.
The aerosol loading desired as a result of this process step depends somewhat upon the nature of the overall process used. In most applications of aerosol former in accordance with this invention, aerosol former will be applied in at least two stages, the first being the above-described process, which is followed by drying, optional blending with other tobaccos, followed by another aerosol former infusion step, to bring the tobacco to the final desired loading level, as discussed above. In such a case, the desired loading of the aerosol former from the initial infusion step is about 20% to 40% by weight, preferably about 25% to 35% by weight, most preferably about 30% by weight.
Once a desired level of aerosol former is achieved in the shredded tobacco, the material is dried to reduce the moisture content to an acceptable level. Preferably this is done in a continuous oven, with the impregnated tobacco being exposed to air in a temperature range which is high enough to reduce the moisture content, without driving off a substantial portion of the aerosol former from the tobacco. Preferably the tobacco is dried in a continuous forced hot air oven, under conditions such that the tobacco temperature can reach up to about 175xc2x0 F.
In the preferred method, where aerosol former is added in two stages, it is preferable to dry the treated tobacco to a moisture content of about 5%-15% by weight, preferably about 8%-12% by weight.
After drying, the loaded tobacco can be equilibrated for a period of time at room temperature and relative humidity, before the next treatment stage. At this time, also, other, untreated tobacco or tobacco materials may be blended with the treated material, for flavor or ease of manufacture. For example, about 5% to 15% of burley tobacco, Turkish tobacco, or reconstituted tobacco sheet can be blended with the treated tobacco.
The next stage is a further treatment in a casing drum, followed by cutting the shredded treated tobacco prior to manufacture of the finished substrate. The treated tobacco, with or without the blended, non-treated tobacco, is treated in a casing drum with aerosol former solution as described above to the point where 3% to 15% by weight of additional aerosol former is infused into the material. The aerosol former materials and conditions are preferably as described above for the first stage infusion. The amount of aerosol former contained in the resulting tobacco substrate is from about 25% to about 50% by weight, preferably from about 30% to about 40% by weight. The resulting material also has a substantial amount of moisture at this stage, e.g., 15% to 25% by weight.
The resulting tobacco substrate material is fed to a standard tobacco cutter, and cut, e.g., at 28 cuts per inch.
From the cutter, the cut tobacco substrate is then dried to below about 6% by weight moisture, preferably to about 3% to 4% by weight moisture, preferably without driving off a substantial portion of the aerosol former from the tobacco. Preferably the tobacco is dried in a continuous forced hot air oven, under conditions such that the tobacco temperature does not exceed about 175xc2x0 F.
Once dried, the cut tobacco substrate is ready to be formed into rod shape, circumscribed with a wrapper, cut into substrate elements, and then combined with fuel elements and other structures to make the completed smoking device, as further described below.
As described above, the preferred smoking article includes a short (i.e., less than about 30 mm in length prior to smoking) preferably carbonaceous, combustible fuel element. Typically, the fuel element is an extruded mass, about 12 mm in length and about 4.2 mm in diameter which is provided with a plurality of longitudinally extending passageways, i.e., defined longitudinal hole(s) passing through the inner portion of the fuel element, and/or grooves located on the periphery of the fuel element.
The passageways provide a surface area which assists in the lighting of the fuel element, and in maintaining burning of the fuel element during smolder. The passageways also aid in controlling the heat transfer from the fuel element to the aerosol generating means. The density of a typical fuel element ranges from about 0.8 to about 1.3 g/cc. Fuel elements of this type are well known in this art.
Typically, the fuel element may be circumscribed by an insulating material in the form of a jacket. Jackets of this type are well known in the art, and a preferred jacket used herein includes alternating layers of glass fibers and tobacco paper.
The cigarette further includes an aerosol generating means which includes the substrate made in accordance with the present invention, which bears at least one aerosol forming material, and which is formed into a continuous rod or substrate tube assembly on a conventional cigarette making machine. Typically the overwrap material for the rod is a barrier material such as a paper foil laminate. The foil serves as a barrier, and is located on the inside of the overwrap.
The barrier material for making the tube aids in preventing migration of the aerosol former to other components of the cigarette. The barrier material forming the tube is typically a relatively stiff material so that when formed into a tube it will maintain its shape and will not collapse during manufacture and use of the cigarette.
An appropriate length of the jacketed fuel element is combined with a substrate section or substrate tube assembly by a wrapper material, which has a propensity not to burn, to form a fuel/substrate section. In preferred embodiments of the cigarettes, the wrapper typically extends from the mouthend of the substrate section, over a portion of the jacketed fuel element, whereby it is spaced from the lighting end of the fuel element. The wrapper material assist in limiting the amount of oxygen which will reach the burning portion of the fuel element during use, preferably thereby causing the fuel element to extinguish after an appropriate number of puffs. In especially preferred embodiments of the cigarette, the wrapper is a paper/foil/paper laminate. The foil provides a path to assist in dissipating or transferring the heat generated by the fuel element during use. The jacketed fuel element and the substrate section are joined by the overwrap.
The preferred cigarette smoking articles of the present invention also include a roll or charge of tobacco, normally in cut filler form, wrapped in a wrapping material such as paper, thereby forming a tobacco rod, and joined by the wrapped paper to the mouthend of the aerosol generating means. A preferred tobacco roll is formed from cut filler comprising a reconstituted tobacco material. Alternatively, the tobacco charge can be in another processed form, such as volume expanded cut filler or aqueous extracted/volume expanded cut filler.
Preferred smoking articles also include a mouthend piece for delivering aerosol to the smoker, which in the case of cigarettes, typically have a tubular shape. However, the mouthend piece may be provided separately, e.g., in the form of a cigarette holder, or as a pipe. The mouthend piece of the preferred smoking articles typically includes a filter plug segment. Preferred filter segments exhibit low filtration efficiencies so as to minimize interference with the passage of aerosol from the aerosol generating means to the mouth of the smoker during draw (i.e., upon use). A segment of flavor-containing material, such as a loosely gathered or pleated tobacco paper or menthol-containing pleated carbon filled sheet can be included between the aerosol generating means and the filter segment. Examples of suitable mouthend pieces are well known in this art.